Hydraulic amplifier



Jan. 13, 1970 Filed June 13. 1968 F. OsTw'A-LD ETAl.

HYDRAULIC AMPLIFIER In K) IO Ila 27 FRITZ Y HEINRICH MICHEL Sheets-Sheet l INVENTOR. OSTWALD ATTORNEY 3, 1970 F. OSTWALD ETA'L 3,488,958

HYDRAULIC AMPLIFIER Filed June 13. 1968 5 Sheets-Sheet 2 F i G 2 4| 22) CLUTCH CONTROLLING SERVO FOLLOWER i F l G 3 Cnniribuflon Pedal of Pressure l Accumulator I d Contribution of a b I c I CluTch pedal l| I Valve T'Hol/" l I I i edul stroke Prehmmcry Phzy clutch play I clutch operohng p 1" range CommencemenT INVENTOR. of clutch stroke F Z OSTWALD y HEINRICH MICHEL TTORNEY Jan. 13, 1970 F. OSTWALD ETAL 3,488,958

HYDRAULIC AMPLIFIER Filed June 13. 1968 3 51 1 5 D Q N (D INVENTOR.

FRITZ OSTWALD BY HEINRICH CHEL "ATTORNEY United States Patent Int. Cl. F156 3/00, 7/00 US. Cl. 6054.5 10 Claims ABSTRACT OF THE DISCLOSURE A hydraulic amplifier for automotive clutches and other loads in which the output is controlled by valves which admit fluid to the load chamber directly, at least initially, and then close off this chamber and apply pressure thereto of both a reservoir and the actuation via a piston.

Our present invention relates to an hydraulic amplifier or pressure multiplier or adder and, more particularly, an amplifier of the character described for automotive clutches and the like.

In prior hydraulic amplifiers, a control valve in the transmission line between the entry and output ports is designed to block the flow at increasing pressure and provide a pressure chamber to which the pressure from a main and an auxiliary pressure source is transferred. In general the main pressure can be supplied by a servocontrol master (e.g. a lever or pedal operated master cylinder) while the auxiliary pressure supply is a hydropneumatic or spring-loaded accumulator.

Force amplifiers of this type have several drawbacks. They need movable force-transmitting members which are troublesome. The substantial pressure diiference between the individual chambers, conduits and passages subjects the interposed sealing means to considerable wear. Further, such amplifiers generally have large dimensions and an intricate structure which makes them expensive to build and to maintain.

It is, therefore, the primary object of our invention to overcome the drawbacks of earlier systems and to provide a compact, reliable and eflicient hydraulic-pressure amplifier.

Another object is to provide an amplifier of the aforementioned type in which movable transmission lines are obviated.

A further object is to provide a simple amplifier which can be produced at low cost.

These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, in an amplifier having a cylinder open at one end receiving a slidable piston which combines the functions of a force transmitter and a valve seat.

Thus, in accordance with the present invention, the hydraulic amplifier has a fluid-output pressure which, at least after an initial increase in step with the hydraulic pressure increase at an actuator input, is augmented by pressure from a hydraulic accumulator or other forcestoring means, the system being adapted for use in hydraulic clutches, fluid couplings, or the like.

The basic structure of the hydraulic amplifier includes a housing forming a cylinder bore which is subdivided by a force-transferring piston into an output chamber communicating with a load on one side of this piston. On the other side of this piston, an annular input compartment is adapted to communicate with a power source such as the hydraulic accumulator mentioned earlier and a central input compartment communicating with a hydraulic actuator (e.g. a master cylinder operated by the coupling lever).

Within this piston, we have provided a valved port connecting the actuator input compartment with the output chamber in the initial stages of operation of the hydraulic amplifier whereby fluid can be displaced from theactuator through the piston into the output chamber for delivery to the load at a rate of p essure increase corresponding to the pressure increase at the actuator. This initial movement suflices to take up the play in the clutch or fluid coupling and is followed by an increase in the resistance of the load.

According to an important feature of this invention, the housing also contains a piston exposed to pressure at the actuator or second input compartment and adapted to control a valve member connecting the hydraulic accumulator with the annular or first compartment. As the pressure builds up on both sides of the force-transmitting piston, the latter is displaced in the direction of the output chamber to close the valved port and thereby block further direct communication between the inner compartment and the output chamber, whereupon operation of the delayed-operation valve connects the forcestorage accumulator with the outer chamber and thereby augments the force supplied to the piston. In this stage of the operation, the force-transmitting piston acts as a membrane and indirectly transfers force to the fluid in the output chamber.

A highly compact structure of the character described can be formed when the housing comprises three axially nested members including a general cylindrical casing defining the cylinder bore and receiving the cup-shaped force-transmitting system, and a central body coaxial with the casing and stepped so as to fit sealingly within the cup of the piston and define within the cup the inner or actuator compartment mentioned earlier. In an annular clearance between this step of the central member and the inner wall of the cylindrical casing, there is formed the outer annular compartment into which the cylindrical wall of the piston cup fits.

The central member, moreover, receives a reaction piston i which bears upon the longitudinally extending valve stem via a resilient member while the stem has .a valve body remote from the reaction piston and received in a chamber formed between the end plate of the housing and the central body. A valve seat in this latter chamber cooperates with the valve body to block fluid flow from the hydraulic accumulator to the annular compartment or permit such flow upon displacement of the valve stem. A check valve in the diflerential piston is normally biased into a closed condition to restrict fluid flow through this piston, the valve member cooperating with a pin carried by the central housing member in the initial position of the piston to retain the valve open and allow such flow.

In one embodiment of my invention of significant compactness the piston is formed as a cup surrounding a central bore. The disk-shaped inner face of the cup at least partially defines one wall of a pressure chamber. The annular surface of the open end of the cup, between the inner cylinder wall and the piston bore, forms one wall of another pressure chamber. A scalable bore passing through the center of the cup bottom leads into the output pressure chamber which is formed by the diskshaped piston bottom and the juxtaposed cylinder base. A peripheral groove in the cylinder wall, proximate to its open end, forms the seat for one section of a tubular sleeve of stepped outer diameter. The sleeve section fitting into the groove represents about one-third of the total sleeve length. A shoulder, juxtaposed with the base of the groove forms the transition to the adjoining sleeve section, comprising also about one-third of the total length which has a reduced outer diameter and is received in the interior of the cylinder. A second shoulder, defining the last third of the sleevelength further decreases the outer diameter, so that the sleeve is insertable into the cup-shaped piston. The second shoulder forms a boundary for the annular pressure compartment, referred to hereinafter as the second pressure chamber, which is also delimited by the inner wall of the cylinder and by'the annular surface of the piston cup. The arrangement not only contributes to the efficiency of the piston motion but provides very satisfactory sealing means between compartments under different pressure which are at least in part in communication with passages in the centred tubular member or sleeve serving for the transmission of pressurized fluid. A packing ring received in a groove of the piston and designed to seal off the second pressure chainber is exposed to relatively minor stress since there is in general only a small difference between the auxiliary pressure led into the second chamber and the total pressure in the output or third chamber.

Another feature of our invention, which obviates threaded connecting means, provides a central bore passing through the sleeve in concentric alignment with the piston bore, has a stepped cross-section throughout its length. In the interior of the piston the sleeve bore fittingly surrounds a slidable control or reaction piston extending coaxially with the main piston. The adjoining part of the sleeve bore extending toward the open cylinder end, has a narrower cross section and houses the slidable control valve proximal to and actuatable by the control or reaction piston. The first input chamber, referred to hereinafter also as the first pressure chamber, which, as previously described is bounded in part by the disk-shaped inner face of the piston is further delimited by the juxtaposed outer face of the control piston slidable in 'the sleeve bone. A passage leading from the center of the piston base into the output or third chamber can be closed off by valve means. The comparatively large contact areas between the inner surface of the sleeve lining the main piston, and the outer surface of the control piston form supplementary seals between the second and the third pressure chambers.

Another feature of our invention provides that the control valve has, at its end proximal to the cylinder end flange, a funnel-shaped flared valve body which is substantially thicker there than throughout the adjoining tubular valve section. Near the transition area where the straight valve part leads to the flared part an annular groove in the valve wall forms a narrow compartment between the straight valve section and the surrounding sleeve. Another compartment surrounding the funnelshaped valve end is in communication with the second pressure chamber. The described structure subjects the valve only to relatively minor stresses even if auxiliary fluid under higher pressure is admitted. The proximal control valve, has a diameter which is somewhat larger than the outer diameter of the valve and is filled, at least in part, with resilient material.

The above and other objects, features and advantages of our invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which:

FIG. 1 is an axial longitudinal cross-sectional view of a fluid amplifier according to my invention;

FIG. 2 is a plan view of the invention shown in FIG. 1;

FIG. 3 is a graph diagrammatically illustrating the phases of operation of the device; and

FIG. 4 is a cross-sectional view similar to FIG. 1 but illustrating a position of the piston in which its valved port is closed.

In FIG. 1 we show the housing of a hydraulic amplifier formed by the concentric and coaxial assembly of a cylindrical casing 17 open at one end 17a and constituting the female member of the housing, a sleeve 16 lining the inner surface 17b and received in the cylinder bore 28,

while constituting the male member, and an end flange 39 or coverplate attached to the sleeve member 16 at its end remote from the closed side of the casing 17. The three elementsthe cylinder, sleeve and end flangeare interconnected by screws 42 which are theradedly received in bores 43 in the cylinder extending parallel to the cylinder axis.

The cylinder bore 28, between the end 19 of the sleeve member 16 and the end wall 33 of the cylinder 17 defines a compartment 14, constituting the output chamber of the device and connected to a load, e.g. a hydraulically operable clutch C, a hydraulically operable torque coupling or the like, via an output port 2 formed in a boss 2a projecting from the closed end of the casing 17. An axially shiftable piston 11 is received in the bore 28 and serves both as a valve-carrying member and a pressuretransmitting member as will be apparent hereinafter. The forward face 21 of the piston 11 is exposed to the output pressure in chamber 14 and is provided with an axially extending boss 55 formed with an axially extending bore 60 defining a chamber within the piston. A spring 34 coaxially surrounds the boss 55 and is centered thereby, while bearing axially upon the Wall 33 and the piston 11 so as to resist displacement of the piston in the forward direction (arrow A). An end face 63 of the boss 55 is engageable with the wall 33 to stop further displacement of the piston 11 beyond he predetermined stroke f the latter established between the end face 19 of member 16 and the end wall 33 of the cylinder bore 28.

The piston 11 is generally cup-shaped and thus includes an axially extending cylindrical wall 11a extending snuggly but slidably along the cylindrical wall 17b of the cylinder bore 28 and provided with a circumferential recess 69 receiving a sealing ring 30 preventing direct fluid transfer between the output chamber 14 and an annular input chamber 10. The latter is defined between the annular end face 23 of the cylindrical wall 11a of piston 11 and an annular cylinder 29 between the small-diameter forward step 16a of member 16 and its intermediatediameter step 16b. The outer wall 16a of the smallerdiameter step thus defines with the inner wall 17b of the casing 17, an annular cylindrical clearance which receives the wall 11a of piston 11 and forms the chamber 10 of variable capacity. In the rest position of the device, the end wall 19 of the small-diameter step 16a bottoms against the interior of the cup-shaped piston as shown in FIG. 1. A circumferential groove 68 is provided in the small-diameter step 16a, close to the end face 19, to sealingly engage the inner surface 22 of wall 11a of the piston, while the latter lies in surface engagement over a relatively long portion of the length of the surface 16a to ensure efficient sealing action.,

The seal 27 closes off the chamber 10 from a further input chamber 15 formed axially in the forward end of the small-diameter step 16a and opening at 15a in the direction of the piston 11. An orifice 29 communicates between the bore 60 and the chamber 15.

As indicated earlier, the piston 11 is a valve-carrying member whose check valve is constituted by a ball 12 engageable with a valve seat 12a surrounding the orifice 29 but held away from the latter by the end 24 of a pin 59 formed integrally upon an aperture disk 35 locked on the member 16 and projecting beyond the face 19 as shown in FIG. 1. The locking means comprises a snap ring 47 received in a groove ahead of the disk 35 which, in turn, is received in an internal peripheral groove 64 defining a shoulder 64 against which the disk 35 bears. The aperture of disk 35, angularly spaced about the pin 59 and extending in axial direction outwardly of the end face 26 of a control piston 3, are designated at 58. A guide cage 49 is axially shiftable within the cylindrical portion 60a of axial bore 60 and is urged by a spring 13 to the left (arrow B) so as to bias the ball 12 against the seat 12a. The spring 13, in turn, bears against a seating washer 15a held in its axially open internal recess 66 by a snap ring 51 fitted into the circumferential groove 66a. Spring 13 has a force which is less than that of spring 34.

A hydraulic reaction force, generated in the input chamber 15 of the actuator, is applied to the control piston 3 which is axially slidable in a cylinder bore 160 opening into the chamber 15 and is formed with a circumferential groove 73 receiving the sealing ring 31 in slidable engagement with the wall 16c. An axially extending recess 4 is provided in the rear end of piston 3 and receives an elasto'meric cushion 4;; which is sealingly engaged by the forward end 75 of a tubular valve stem 5 received with clearance at 5a in the recess 4 so that, upon separation of the end 75 from the elastomeric cushion 4a, a return flow of fluid can pass through the clearance 5a into the chamber 70 beyond the piston 3. Chamber 70 has a diameter slightly in excess of that of piston 3 while an annular enlargement 32 of chamber 15 surrounds the forward end of this piston and communicates with an inlet passage 18. The latter passes through member 16 to its rearmost face 16d overlain by the cover plate 39 mentioned earlier. A sealing washer 45 is sandwiched between the latter and the end face 16d to prevent escape of hydraulic fluid supplied to the chamber 15 via an inlet port 1 formed in member 39.

The inlet port 1 is connected to a source of hydraulic fluid such as a servomaster cylinder M operated by a lever or pedal P. The cover plate 39 has a cylindrical forwardly extending axial boss 56 received movably in a rearwardly open cylindrical recess 71 in the large-diameter step 16e of member 16, this large-diameter step forming an annular flange 21 which is clamped between the plate 39 and a large-diameter step 54a of the wall 54 of casing 17. A seal 46 is provided in an annular recess 56' at the junction of the end wall 61 of casing 17 and the cylindrical wall 17b, and engages the wall 58 to prevent escape of fluid between member 16 and 17. Similarly, seals 71a and 9a are located between the forward end 56a of boss 56 and the rearward face 16 of the largediameter step 166 and between the end face 16d and the front face 39a to prevent leakage of fluid from a pair of passages 53a and 9b, respectively. A central triangular projection 52 of relatively thick section is provided on the flange 39 to facilitate connection of the various fittings to this flange at the actuator inlet port 1 and at a pair of ports 9 and 53, respectively. Port 9 communicates with a source of added fluid pressure such as a hydraulic accumulator H adapted to sustain relatively high auxiliary pressures. The accumulator may be of the type described in Fluid Power, US. Government Printing Office, Washington, DC 1966. The accumulator may be part of a hydraulic system whose pump p serves to operate in the hydraulic loads (eg via the branch L) and draws fluid from the reservoir R to which fluid is returned from the port 53.

The high hydraulic pressure of inlet 9 is delivered via passage 9b to a passage 7 formed in the large-diameter step 16e of the guide sleeve 16, the passage 7 delivering the fluid to an annular compartment 37 formed in I a guide bore 5b of sleeve 16 and slidably receiving the valve member 5 previously mentioned. A circumferential groove 44a in the inner wall of bore 5b receives a seal 44 in slidable engagement with the smooth shank of the valve member 5 which is stepped at its end remote from the control piston 3 to form the compartment 37. In the region in which the bore 5b meets the face 16 there is formed a valve seat 50 engageable by the conical valve body 36 of the valve member 5 at this end. The valve member 5 is urged to the right (arrow D) by a spring 6 seated against a forwardly facing surface 73 of a chamber 8 in the boss 56. Chamber 8 opens in the direction of arrows A and D. A further passage 20 connects the chamber 8 with the annular compartment 10 adapted to apply pressure to the end face 23 of the piston wall 11a. From the chamber 70, a passage 80 leads to the passage 53a of the return port 53. Fluid from chamber 8 can be returned to the reservoir R via the axially extending central bore 40 in valve member 5, the clearance 5a and the chamber 70 while leakage from chamber 8 is prevented by the sealing ring 38 received in the inwardly open circumferential groove 57 along the wall 72 of the recess accommodating boss 56. Axially extending bores 41 at the vertices of the angular flange 39 allow the latter to be secured to a support structure.

The hydraulic amplifier of FIGS. 1, 2 and 4 is shown in its rest position in FIG. 1 in which the spring 35 retains the piston 11 in its extreme left-hand position in which the cup of the piston bottoms against the abutment surface 19 and the pin 59 holds the ball 12 out of engagement with its seat 12a. Since communication is established between the master cylinder M or other hydraulically actuated load C (via an inlet port 1, the passage 18, the annular enlargement 32, compartment 15, orifices 48, aperture 29, bore 60, chamber 14 and outlet port 2) the amplifier in its rest position is always ready for operation.

Upon actuation of the coupling lever, the servo-cylinder M thereof progressively increases the pressure at the inlet port 1, thereby increasing the pressure at chamber 15, in outlet chamber 14 and at the load C substantially along the diagrammatic characteristic line a of FIG. 3. As the hydraulic cylinder at the clutch C senses the increasing mechanical resistance to the actuation pressure (corresponding to the preliminary pedal play represented along the ordinate of the curve of FIG. 3), the piston 3 is displaced to the left (arrow E) as a consequence of the increased pressure in chamber 15 to compress the elastomeric mass 4a and bring the latter into contact with the front end 75 of the valve member 5 (region b of the graph). When the pressure chamber 15 suflices to overcome the force of spring 6 against the valve 5, the valve body 36 of the latter is lifted from the seat 5c (point 0 of the graph corresponding to the valve threshold), thereby connectig the accumulator H with chamber 10 via the input port 9, passages 9b and 7, compartment 37, chamber 8 and passage 20. The piston 11 thus receives a pressure to the right (arrow A) corresponding to the sum of the pressures developed in chambers 10 and 15 (corresponding to region d of the graph) whereby the piston 11 is displaced to the right against the force of spring 34. Valve 12 closes (FIG. 4) and further increases in pressure at chamber 14 is indirect and via the intermediary of the piston now acting like a diaphragm. Further increase of pedal pressure (region e of the graph) produces a corresponding increase in the pressure in chamber 14 in accordance with the relationship where P is the output pressure generated in chamber 14 and delivered to the load, P is the input pressure at port 1 and chamber 15 at which the valve 12 rests its seat 12a, AP, is the subsequent increase in input pressure at port 1 and chamber 15 and P is the pressure of the hydraulic accumulator as applied to surface 23, P P and P being weighted in accordance with the respective surface areas.

Upon release of the input pressure at chamber 15, spring 34 urges the piston 11 to the left until the pin 59 again lists the ball 12 from its seat 12a. Spring 6 urges the valve member 5 to the right until the valve body 36 engages the seat 5c. The accumulator pressure, which may be between 20 and 350 atmospheres gauge, is applied via bore 40 to the piston 3 and thereby lifts the elastomer 4a from the forward end 75 of the valve 5 and relieves the pressure in chamber 10 via the passage 20, the chamber 8, chamber 70, passages and 53a and the port 53 to the reservoir R. The system is thus restored to its rest condition (FIG. 1).

We claim:

1. A hydraulic amplifier comprising housing means forming a cylinder; a piston slidably displaceable in said cylinder and defining on one side of said piston an output chamber and on the opposite side of said piston a pair of independent input chambers including a first input chamber connectable with a source of actuating fluid pressure, and a second input chamber connectable with an auxiliary source of fluid pressure; means for connecting said output chamber to a load; and valve means controlled by the pressure in said first input chamber and communicating between said second input chamber and said auxiliary source for applying the pressure of said auxiliary source to said piston upon the pressure in said first input chamber attaining a predetermined level.

2. A hydraulic amplifier as defined in claim 1 wherein said housing means comprises a generally cylindrical casing forming said cylinder and receiving said piston, and a central guide member having a cylindrical step defining with the inner wall of said casing a cylindrical clearance, said piston being generally cup-shaped and having a cylindrical wall received in said clearance and defining said second input chamber therein, said guide member defining, with the interior of the cup of said piston, said first input chamber.

3. A hydraulic amplifier as defined in claim 2 whereinsaid valve means includes a control piston axially shiftable in said guide member in a direction opposite the direction of displacement of the first-mentioned piston under fluid pressure in said first input chamber, and a valve member shiftable by said control piston for interconnecting said second input chamber and said auxiliary source of fluid pressure.

4. A hydraulic amplifier as defined in claim 3 wherein said first piston is provided with second valve means operable independently of the first-mentioned valve means and having an open-condition interconnecting said first input chamber and said output chamber in a rest position of said first position by blocking fluid flow between said first input chamber and said output chamber upon movement of said first piston out of said rest position.

5. A hydraulic amplifier as defined in claim 3 wherein said second piston defines with said guide member a compartment remote from said first input chamber and connectable with a fluid reservoir, said second piston being provided with an elastomeric cushion engageable with said valve member to prevent fluid flow into said compartment upon displacement of said valve member by said first piston but withd'rawable from said valve member to relieve pressure in said second input chamber.

6. A hydraulic amplifier as defined in claimv 5 wherein said housing means is formed with a valve compartment having a seat engageable by said valve member and com- 'municating with said second input chamber, said valve member being tubular and opening into said valve compartment and in the direction of said second piston while defining in said guide member an annular compartment: connected with said auxiliary source and connectable with said valve compartment upon displacement of said valve member in a direction opposite the direction of displacement of said first piston from its rest position.

7. A hydraulic amplifier as defined in claim 6 wherein said housing means comprises a cover plate formed with said valve compartment, said first valve means further comprising a spring biasing said valve member into engagement with said seat.

8. A hydraulic amplifier as defined in claim 4 wherein. said second valve means includes a valve member carriedl by said first piston, spring means biasing the valve member of said second valve means in a direction opposite the direction of displacement of said first piston out of its rest position, said first piston defining a valve seat engageable by the valve member of said second valve means upon movement of said first piston from said rest position, and means on said guide member engageable with said valve member of said second valve means for retaining same in said open condition in said rest position of said piston.

9. A hydraulic amplifier as defined in claim 8, further comprising a spring in said output chamber bearing upon said first piston and urging same into said rest position.

10. A hydraulic amplifier as defined in claim 9 wherein said first and second pistons are each provided with respective annular seals slidably engageable With inner walls of said cylinder and said guide member respectively, said guide member is formed with a circumferential seal slidably engaging the inner wall of the cup of said first piston, and said valve members, pistons and chambers are coaxial with one another.

References Cited UNITED STATES PATENTS 1,885,235 11/1932 Davis.

2,351,872 6/ 1944 Parker.

2,402,344 6/ 1946' Price.

2,403,912 7/1946 Doll.

2,443,642 6/ 1948 Rockwell.

2,499,563 3/1950* Bill.

2,827,766 3/1958 Huflord.

MARTIN P. SCHWADRON, Primary Examiner ROBERT -R. BUNEVICH, Assistant Examiner US. Cl. X.R. 

